The object of the proposed research is to clarify the specific molecular mechanisms of hormone-protein interactions. Systematic studies of the binding of polypeptide and steroid hormones to their physiological receptors will yield valuable information about the structural requirements of the ligand for binding, conformational changes which occur upon hormone binding to a protein, and the way in which these interactions can be modified by changing the nature of either the hormone or the binding protein. Three hormones chosen for study are: 1) oxytocin, a peptide hormone which regulates lactation and the initiation of parturition; 2) vasopressin, a peptide which regulates water balance; and 3) estradiol, the female sex hormone which modulates female reproductive functions. The interaction of oxytocin and vasopressin with neurophysin, a protein which is located in granules of the posterior pituitary where these hormones are stored prior to secretion, will be studied using stopped-flow temperature-jump relaxation kinetic techniques. By use of modified neurophysin and analogues of oxytocin and vasopressin, we shall identify the role of specific amino acid residues which are located at or near the binding site. The binding of estradiol to alpha-fetoprotein, a serum protein synthesized in early fetal development and in some hepatic and malignant disease, will be investigated using fluorescence spectroscopy and fluorescence stopped-flow techniques. Information obtained from the alpha-fetoprotein binding system will be extrapolated to help define the nature of the initial complex formed between a steroid hormone and its specific cytoplasmic target cell receptor. To provide further evidence to confirm the general nature of our model for the role of metal ions in the biological actions of oxytocin, we shall examine the thermodynamics and kinetics of oxytocin binding to a uterine particulate preparation; for these experiments we shall use a previously developed radioligand hormone receptor assay system. Laser Raman Spectroscopy will be used to assess the effects of the biologically active divalent metal ions on the conformation of oxytocin in solution.